JPH01244420A - Optical beam scanner - Google Patents

Abstract

PURPOSE:To reduce the incident radius of an optical beam so that a hologram disk can be miniaturized and an arbitrary image forming distance can be obtained by using coma waves produced when stigmatic waves are made incident on a spherical optical element from the outside of its optical axis as the object wave for producing the hologram disk. CONSTITUTION:Coma waves emitted when stigmatic spherical waves are made incident on a spherical optical element 10 from the outside of its optical axis are used as the object wave for producing the hologram of a hologram disk 4. When the hologram disk 4 produced in such way, a hologram lens 3, and a semiconductor laser 2 for irradiating a reproducing optical beam are used, the incident radius R in the radial direction from the axis of rotation of the disk 4 can be made shorter and the disk 4 can be miniaturized. In addition, an arbitrary image forming distance l can be obtained irrespectively of the disk producing wavelength.

Description

[Detailed Description of the Invention] [Summary] Regarding a light beam scanning device using a hologram disk, the purpose of the present invention is to obtain a hologram disk in which the aberration of the scanning beam is small in the entire scanning area and which is smaller than conventional ones. In a light beam scanning device that scans a light beam by using an object wave, which is one of the waves for creating a hologram of the disk, the imaging distance becomes shorter toward the outside of the disk along the radial direction from the central axis of rotation of the disk. and a rotating object having a hologram created by irradiating a comatic aberration wave with different imaging distances in a direction orthogonal to the radial direction, and a reproduction light beam irradiation light source that irradiates a reproduction light beam; The output light is thereby diffracted in accordance with the rotation of the rotating object. [Field of Industrial Application] The present invention relates to a light beam scanning device using a hologram disk.

Recently, light beam scanning devices using holograms, which have a simple structure and are easy to manufacture, are being used instead of complex and expensive rotating polygon mirrors for barcode reading and laser beam scanning in laser printers. There is a demand for a compact optical beam scanning device with small beam aberrations.

[Conventional technology]

Conventional optical beam scanners for high-precision linear scanning, such as those used in laser printers, have used polygon mirrors, but they had the disadvantage of being expensive due to poor processing accuracy and the use of tilt correction optical systems. .

In response, testing of optical beam scanners using hologram disks is underway.

In particular, in light beam scanners using this hologram disk, so-called "self-imaging" light beam scanners that do not use auxiliary optical systems such as f-theta lenses after exiting from the disk are inexpensive due to their simple configuration. It has advantages.

[Problem to be solved by the invention]

However, the above-mentioned conventional technology is limited in terms of miniaturization and freedom of design of the hologram disk. This will be explained using patent application number 59-48076 for a hologram disk manufacturing method filed by the present applicant.

This preparation method is shown in FIG. The design parameters of the hologram disk 4 for linear scanning include two diverging spherical wave light sources Δt when creating the hologram, and the distance from the disk to 82 f111 ``” f l+2 + the wavelength to be created λ1. and the distance R from the disc incidence point P to the two light sources Δ1 and A2 during reproduction, the disc incidence angle θj, the reproduction wavelength λ2. shall be. In particular, the incident angle θi is determined by the following equation.

...(1).

The disk is designed using the above design parameters, but
A particularly important parameter is the ratio of wavelengths during playback and creation λ”
2/λ1. In other words, it is essential to use a laser beam with good coherence as a light source when creating a hologram, but the types of this laser are also limited. Therefore, the design of a disk with the required characteristics must also be discrete. FIG. 12 illustrates this situation. In FIG. 12, the reproduction wavelength λ2 is fixed to the semiconductor laser wavelength of 780 nm, and the disc creation wavelength λ1 is fixed to the commonly used 488 nm.
m (Ar laser), 441.6 nm (He-C
d laser).

This figure shows the disk incidence radius R and the imaging distance β to the imaging plane when a linear scanning disk is designed using a 325 nm (He-Cd laser).

From this figure, in order to make the disk smaller while keeping the imaging distance ρ constant, that is, to make the incident radius R smaller, the wavelength λ1 at the time of production can be made smaller (but there is a limit. If you reduce , the imaging distance will become smaller, so
In particular, when scanning a wide area, it is necessary to perform more enlarged scanning, which has the disadvantage of deteriorating the linearity of the scanning trajectory and increasing the aberration of the scanning beam, making it difficult to apply to high-precision scanning such as laser printers. Ta.

In view of the above points, the present invention makes it possible to reduce the incident radius R, that is, to miniaturize the disk, and to obtain an arbitrary imaging distance l without being limited by the disk production wavelength λ1, and to make the scanning trajectory straight. Not only is it compact, but it also significantly reduces scanning beam aberration.

An object of the present invention is to provide a light beam scanning device using a high-resolution hologram disk.

[Means to solve the problem]

The object of the present invention is to provide an optical beam scanning device that performs optical beam scanning using a hologram disk according to the present invention. A rotating object with a hologram created by irradiating a comatic aberration wave whose imaging distance becomes shorter toward the outside of the disk and whose imaging distance in a direction orthogonal to the radial direction also differs, and a reproduction light beam. This is achieved by a light beam scanning device that is equipped with a reproduction light beam irradiation light source that irradiates a reproducing light beam, and thereby scans an emitted light beam that is diffracted according to the rotation of the rotating object.

[For production]

It uses comatic aberration waves that are generated by entering from off-axis of the element. Therefore, it is possible to reduce the light beam incidence radius R, that is, to make the disk smaller, and to obtain an arbitrary imaging distance β without being limited by the hologram disk creation wavelength λ, and to significantly reduce the aberration of the scanning beam. small size,
A light beam scanning device using a high-resolution bologram disk can be realized.

〔Example〕

Hereinafter, embodiments of the present invention will be described in detail.

A light beam scanning device for linear scanning will be explained using Japanese Patent Application No. 168830/1989 filed by the present applicant. As shown in FIG. 11 again, this is a simple optical beam scanner consisting of a semiconductor laser 2 as a light source, a hologram lens 3 for aberration correction, and a hologram disk 4. A light beam 6 incident from one side of the hologram disk 4 is diffracted by the hologram and scans the second side of the drum 5 as an output beam 7 as the hologram disk 4 rotates.

Note that this hologram disk 4 uses the technique disclosed in Japanese Patent Application No. 51-48076 mentioned above.

Here, we consider miniaturizing the disk in order to make the device more compact and to lower the cost. In terms of scanning performance, the scanning width is 84
The size is 252 mm, and the resolution is 300 dpi.

Therefore, the scanning beam diameter is targeted to be 100 μm or less. Conventionally, in order to achieve this goal, the design values indicated by ★ in FIG. 12 were required. (This design value is described in the previously filed Japanese Patent Laid-Open No. 62-234118.

) In other words, the diameter of the disk needed to be 100 mm in consideration of the exit diameter of the light beam. Therefore, we are considering reducing the disk area to 65 mm, which is significantly smaller by 50%, while maintaining the above-mentioned scanning performance.

Therefore, let us consider the phase transfer function ψo (x, y) of the hologram disk 4 that provides good linear scanning and a good scanning beam diameter with the incident radius R being 28 mm.

Therefore, the phase transfer function ψH(x, y) of the disk is expressed as ψH(x, y) −Σ c,, x' yj
・ Expands to -12+. (C4, t) is an unknown quantity.

In order to obtain this optimal phase ψ, the present applicant
A part of the method shown in No. 2-240922 is used. In other words, in Fig. 11, the phase ψ1 of the disk's wave resistance is set to ψ,
. (x, y), the phase of the aberration-free scanning beam at each scanning point n is ψ. ut t“l) (X.

y), and if the phase transfer function of the hologram disk being scanned at that time is ψo'(x, y), then
According to No. 2-24.0922, ψin”t(X+y)
- ΣWn (φ out ku' (X+ y
) −φ o ” (X+V)) Σ40 . . . It is known that the aberration of the scanning beam is the smallest evenly when the incident wave satisfies (3).

The optimal incident wave phase ψ,, apt (x,
y) is the disk phase transfer function φIf (X, y
), but this φin. The phase transfer function of the disk (C
Optimize ijl. As a result of finding this using the attenuated least squares method, the linearity of 3 within ±0.1 mm as shown in Figure 10 was obtained.
It has been found that a scanning locus over four formats and a sponoto diagram of the scanning beam from the scanning center to the scanning edge as shown in FIG. 9 can be obtained. Here, the wavelength λ2 to be reproduced is 780 nm of the semiconductor laser, and ψH(X, y) is a complex function with an aspherical term.

As a result, it has been found that the necessary phase transfer function ψH (x, y) exists. Next, a method for actually creating this by holographic exposure will be described.

As shown in FIG. 8, a disk with the required ψH (x, y) is given as an example of λ+ = 325 nm (He-
Let's consider a method of creating the image using a Cd laser. If it is necessary,
When the reference wave is a diverging spherical wave (no aberration) on the hologram 1 and disc in which ψH(X, y) is recorded, the necessary object wave is a complex coma aberration wave 9 as shown in Fig. 8 by ray tracing. It turned out to be. Therefore, as shown in FIG. 1, the aberration-free diverging spherical wave 12 is
It was found that the coma aberration wave when incident from off-axis is an aberration wave with the same tendency, so we decided to use this aberration wave.

Actually, the parameters of this spherical optical element 10 (here, a convex lens) were optimized so that the aberration wave was the same as that shown in FIG. The method at this time is shown in FIG.

Here, the distance R from the center of rotation of the disk to the point of incidence is
28 mm, Borodaram creation wavelength λ1'''325 nm
(He-Cd laser) Distance from reference wave point light source position B1 to disk Fol-115, 126 mm, B+
Distance from to the center of the disk y+ = 5.854 mm
, and the curvature R+ of the convex lens for aberration generation = 17.68
mm, center thickness Dlo, 00 mm, material synthetic quartz, refractive index N 1.483 (325 nm), distance between lens optical axis and disk center Hy = 50 mm, distance between bottom surface of lens and disk 1-t 80 mm .

Point light source position B2 on object wave side and distance between lenses 7!1-9.
983 +nm, distance between B2 and lens optical axis y, -7
, 170mm.

Further, the distance between the point where the principal axis of light emitted from the point light source intersects with the lens and the lens optical axis is yz -5,298 mm.

Also, a method for creating the hologram lens 3 for aberration correction.

Regarding the settings, please refer to the patent application filed by the applicant in 1982-
It may be carried out according to the method described in No. 234118.

Therefore, a detailed explanation will be omitted here, and as shown in FIG. 11, the semiconductor laser 2. Hologram lens 3. Full hologram system consisting of 4 hologram disks, I: J11
However, we will limit ourselves to showing the manufacturing design values of the aberration correcting hologram lens 3 most suitable for this hologram disk using FIG. 3. In FIG. 3, the creation wavelength λ of the hologram lens 3
1=488 nm (Ar laser).

As a parameter of the plano-convex lens 10', the center thickness d
-2,00mm, curvature R=15. OOmm, refractive index 1.5222 (488 nm, material BK-7), L/7 of incident convergent spherical wave, distance f from the top surface of 11 to the convergence position
-31,00m.

Distance j from the top surface of lens 10 to the substrate surface of hologram lens 3! + = 41.57 mm. Also, the material of the plano-concave lens 11 is BK7, and the center thickness DO1 = 20.99.
mm, curvature Rz = 65. OOmm, tilt angle from the hologram substrate α-18.5°, ρ2 = 140
．． 00 mm.

βa = 74.30 mm. Also, convergent spherical wave 1
4B 12 - Optical axis deviation position V z = 20.931 mm, focal length f-111,593 mm, incident angle θ1 = 22.236
It is.

The hologram lens created using the above optical system is shown in Fig. 4 (a ■ mark is added in Figs. 3 and 4 to clearly indicate the setting plane of the hologram lens), and the hologram disk 4 and hologram Distance a of lens 3 = 10.0
mm, and the inclination of the hologram lens is set to 16.975 mm. At this time, of course, the radius R of the disk incidence point on the disk is 28 mm.

FIG. 5 shows a spot diagram of the scanning beam when using the above-mentioned optimal Borodaram disk and hologram lens. Of course, λ2 for playing the disc is 7EiQ nm
The incident angle θi is 42.6166 as described above. The beam aberration is sufficiently small to within 80 μm for 84 format scanning.

Moreover, it agrees well with the spot digram based on the required phase transfer function in FIG. 9.

Furthermore, we conducted a wave optical study when creating this hologram. Figure 6 shows the RMS (λ) of the wavefront aberration of the scanning beam when the scanning beam diameter is set to 100 μm or less and the F number of the scanning beam is approximately 75.
The calculated value is shown below. It can be seen that in order for the scanning beam to be a diffraction-limited system, it needs to be 0.07λ or less, or high-resolution scanning with a sufficient margin is possible.

Further, the scanning locus at this time is shown in FIG. This also coincides with the scanning locus when the necessary phase transfer function ψ is shown in Fig. 10, and the hologram disk according to the present method is almost ideal in terms of high resolution and linear scanning. As described above, according to the present invention, a hologram disk that has been significantly reduced in size can be used to achieve the same level of precision and accuracy as before.
A high-resolution light beam scanning device can be obtained.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of bologram disk production efficiency according to an embodiment of the present invention, FIG. 2 is an explanatory diagram of hologram disc production parameters according to an embodiment of the present invention, and FIG. 3 is an illustration of a bologram for aberration correction according to an embodiment of the present invention. Lens creation optical system explanatory diagram,
FIG. 4 is an explanatory diagram of setting parameters of the all-hologram optical beam scanner. Figure 5 is a spot diagram of the scanning beam;
Figure 6 shows the amount of wavefront aberration due to the hologram according to the embodiment of the present invention, Figure 7 shows the scanning trajectory of the light beam (calculated value), Figure 8 shows an explanation of the waves created on the hologram disk, and Figure 9 is a spot diagram of the scanning beam, and Fig. 10 is the scanning locus of the light beam (calculated value). FIG. 11 is a configuration diagram of an all-hologram type optical beam scanner, and FIG. 12 is an explanatory diagram of design values of a conventional optical beam scanning device.
FIG. 13 shows an explanatory diagram of a conventional light beam scanning device. In the figure, 2 is a semiconductor laser, 3 is a hologram lens, 4 is a hologram disk, and 5 is a drum. 6 is an incident light beam, 7 is an output beam, 9 is a coma aberration wave,
10 is a spherical optical element, 10゛ is a plano-convex lens. Aoi 11 is a plano-concave lens, 12 is a diverging spherical wave, 13 reference-15
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Claims (3)

[Claims] (1) In an optical beam scanning device that performs optical beam scanning using a hologram disk, an object wave, which is one of the hologram creation waves of the disk, is focused toward the outside of the disk along the radial direction from the central axis of rotation of the disk. A rotating object with a hologram created by irradiating a comatic aberration wave with a shorter image distance and a different imaging distance in a direction orthogonal to the radial direction, and a reproducing light beam irradiating the reproducing light beam. A light beam scanning device comprising a light source, whereby an emitted light beam diffracted according to the rotation of the rotating object scans. (2) The light beam scanning device according to claim 1, wherein a wave emitted by inputting an aberration-free spherical wave from outside the optical axis of the spherical optical element is used as the object wave. (3) The wavelength of the hologram creation wave is shorter than the reproduction wavelength, and the reference wave of the hologram creation wave is an aberration-free diverging spherical wave, and the point light source position is the object wave with respect to the center of disk rotation. 3. The light beam scanning device according to claim 2, wherein the light beam scanning device is located at a position opposite to the light beam scanning device.